1. Field of the Invention
The present invention relates to a radio communication apparatus used for a radio receiver such as a cellular phone. Especially, the present invention relates to a circuit system which suppresses an interference wave automatically and is able to transfer data at high speed.
2. Related Background Art
The cellular phone has prevailed rapidly. There are an analog system and a digital system for the cellular phone. The digital system can use frequency band more efficiently than the analog system, and the digital system surpasses the analog system in capability for security. Because of this, it is predicted that the digital system becomes predominant in future.
The digital system converts a voice signal into code information and transfers the information by radio frequency. Because of this, the digital system has a feature in that it hardly suffers the influence of noise. On the other hand, in order to increase the number of channels available for the cellular phone, frequency band per a channel has to be narrowed. However, when the frequency band per a channel is narrowed, each channel easily suffers the influence of the noise. Because of this, a conventional circuit which suppresses an image interference wave by using a quadrature mixer and a .+-.45.degree. phase shifter has been known.
In order to suppress the image interference wave, it is necessary to control a gain difference and a phase difference between an I signal as an in-phase component and a Q signal as a quadrature component. However, the conventional circuit has initially set the gain difference and the phase difference only by hand. The reason is because differential signals of the gain difference and the phase difference is very little, for example, less than 1 dB or 2.degree., and because a technique which detects such a micro signal with high precision and controls the gain difference and the phase difference has not been established. Because of this, the gain difference and the phase difference had to be controlled by hand. Accordingly, it has taken a long time to control the gain difference and the phase difference, and the conventional circuit could not suppress the image interference wave at will.
On the other hand, FIG. 17 is a diagram which explains TDMA (time-division multiple access) in a mobile communication system called a GSM system which is prevailing in Europe. As shown in FIG. 17, the GSM system transfers data at each time-slot. A sending timing fRX of a mobile station (MS) which communicates with a base station and a receiving timing fTX is being shown in FIG. 17.
The mobile station receives the data at a time R1 and sends data at a time T1. The mobile station receives the next data at a time R2 after 8 time-slot of the time R1. Between times R6 and R7, a period which monitors another channel is provided.
The mobile station has to perform both of a voice communication and a data transfer within one time-slot. Because of this, the capability of transferring data is inevitably limited by a time length per one time-slot.
Accordingly, in order to transfer a large amount of data at high speed, a bit rate in a time-slot has to be raised, or data transfer has to be performed by using a plurality of slots. It is difficult to realize the former because of restriction of the conventional system. In the case of the latter, because an interval between the sending period and the receiving period becomes narrow inevitably, a frequency synthesizer used in the radio communication apparatus has to be changed quickly. That is, it is necessary to use an expensive frequency synthesizer.